1. Field of the Invention
The present invention relates to a device and method for mixing a plurality of fluids and dispensing the resultant mixture, wherein a gas is used to force the mixture out of the device. In particular, the present invention relates to a device and method for preparing and dispensing a wound sealant.
2. Description of the Related Art
A number of applications require the mixing of a plurality of fluids immediately before use of the mixture. Examples of such fluids include the components of "fibrin glue" wound sealants, gel components for use in electrophoresis, and the components of epoxy cement. In each of these applications, the components must be combined in appropriate amounts, thoroughly mixed to form a mixture, and dispensed before increased viscosity impairs mixture flow. The basic considerations associated with mixing separate components and immediately dispensing the mixture are exemplified herein by a discussion of the preparation of wound sealants.
Wound sealants are used in the repair of damaged tissues and vessels. In particular, wound sealants are designed to prevent persistent fluid loss from or into a wound, which can increase patient discomfort and morbidity, prolong recovery, and compromise or prevent an otherwise successful outcome.
The problem of fluid leakage is particularly severe in highly vascularized tissues, such as kidney, liver, spleen and cancellous bone, which continue to bleed even after electrocautery. Arterial vascular grafts often leak at sites of anastomosis, along suture lines, and even through the grafts. Dural wounds are extremely difficult to repair, with a 30% failure rate for some of the best currently available procedures. Resection of lung tissue often results in persistent air leaks, which significantly prolong recovery. Moreover, such problems are often exacerbated in patients suffering from diabetes or other disease processes that impair normal wound healing.
The use of wound sealants based on fibrin glue has received widespread attention as a solution to the problem of fluid leakage. Fibrin glue is formed by using a fibrinogen activator, such as thrombin, to cleave fibrinogen to fibrin, followed by formation of a coagulum by fibrin-fibrin crosslinking. Fibrin molecules also form crosslinks with collagen, a principle constituent of most tissues. These fibrin-collagen crosslinks promote adherence of the fibrin clot to the tissue to be sealed.
This approach offers a number of advantages. First, fibrin glues can be prepared from a patient's own blood, thus eliminating the problems of disease transmission and immunological complications associated with the use of donor materials. Second, the rate of coagulum formation can be adjusted to suit the needs of a particular application by adjusting the concentration of fibrinogen activator in the mixture.
Third, fibrin glues are predominantly physiologic in origin, and therefore normal fibrinolytic processes remove the coagulum, typically, within two to three weeks, leaving minimal scarring. If desirable, coagulum breakdown can be slowed by the addition of antifibrinolytics such as .epsilon.-amino caproic acid, tranexamic acid, or aprotinin. Finally, other chemical agents, such as antibiotics or anticancer drugs, can be added to the fibrinogen and or fibrinogen activator solutions before mixing to provide sustained release of the agent at a wound site or selected site of action.
While the benefits of fibrin glue wound sealants are clear, the preparation and use of fibrin glues is complicated by several problems. For example, thorough mixing is required to form a strong adhesive. However, a limited time period is available for mixing, given that coagulation begins immediately upon contact of the fibrinogen solution with the fibrinogen activator solution.
In addition, fibrin glues are typically applied using a syringe-like applicator, in which the coagulating mixture must flow through a relatively small aperture. Any interruption in the flow of the mixture, which is often necessary during wound sealing, can result in formation of a coagulum that plugs the aperture. When this happens, treatment can be continued only by replacing the applicator or, in some devices, clogged applicator parts.
Examples of this type of applicator are disclosed U.S. Pat. No. 4,359,049 (issued Nov. 16, 1982 to Redl et al.) and U.S. Pat. No. 4,735,616 (issued Apr. 5, 1988 to Eibl et al.). In these devices, two syringes are attached at their outlets to a connecting head that provides a separate fluid channel for the contents of each syringe. Mixing occurs in a mixing needle attached to the outlets of the two channels. Clogging of the needle during interruptions in use causes difficulties when a patient requires more than one continuous application of fibrin glue. One embodiment disclosed in U.S. Pat. No. 4,359,049 has a spraying head, rather than a mixing needle, wherein a spray is produced by sterile gas supplied at the outlet of each of the fluid channels.
A variation of this device, described in U.S. Pat. No. 4,631,055 (issued Dec. 23, 1986 to Redl et al.), has a connecting head adapted to connect either to a mixing needle or a multi-lumen catheter. The connecting head includes a third fluid channel for a gas. Each of the channels is designed connect to a separate lumen of the catheter. Thus, fluids in the three channels come together at the inlet of the mixing needle or at the outlet of the catheter.
This design was intended to allow the application of fibrin glue in the form of a liquid or fine spray by varying the relative flow rates of fibrinogen, fibrinogen activator, and gas. However, in practice, a sputtering effect, rather than a fine, even spray, is observed. Furthermore, the catheter embodiment suffers from the disadvantage that mixing occurs in an uncontrolled manner after the fluid streams exit the catheter.
Thus, current preparation and application devices for fibrin glue wound sealants often do not provide adequate mixing of the fibrinogen and fibrinogen activator solutions or do not provide a mechanism for smooth application of the wound sealant mixture. Furthermore, these devices suffer from clogging problems that prevent further use after an interruption in the application process.